Magnetic resonance scanners (MRI) use the physical principle that atomic nuclei in magnetic fields experience a precession movement of the nuclear spin of these atomic nuclei which can be measured and whose characteristic depends on the type of atomic nucleus. Magnetic resonance imaging uses this phenomenon for imaging by magnets, which are usually arranged in the form of a tube or annulus around a patient couch, inducing reactions of the atomic nuclei within the body of the patient, in which case these reactions can be detected by way of detectors and evaluated. Processing of the acquired data results in three dimensional images of the examined body; the images depend on the location within the body and the type of tissue.
Gradient coils (GC) which additionally modulate the applied magnetic field are used in MRIs. These GCs are usually arranged concentrically to a permanent-magnet field ring and generate temporary magnetic fields, developing noise and vibrations in the process. Furthermore, body coils (BC), a specific type of measurement receiver, are also often present and are also arranged concentrically to the other coils. This thus results in a concentric configuration of an MRI comprising a plurality of layers. The configuration of an MRI is known to a person skilled in the art.
Positron emission tomographs (PET) use a different physical principle for imaging inside the patient's body. In this case, a radiopharmaceutical is introduced into the body and can be stored in the most diverse organs and tissues of the body, depending on its respective metabolism. In the decay processes of the respective radionuclide (inter alia, PET uses 18F, 11C, 13N or 15O which emit positrons as they decay) used in the radiopharmaceutical, positrons are emitted which collide with electrons while they are still in the patient's body and are thus annihilated, releasing gamma radiation as secondary radiation in the form of two photons in the process. These photons move apart from each other at an angle of approximately 180°. This secondary radiation can be measured by suitable receivers. These receivers also surround the patient's body in the form of a tube or annulus, similar to the MRI. Generally, PET images lack anatomical information due to the display of metabolic processes or the information is very limited and restricted by the limited spatial resolution (approximately 4-5 mm). For a while, different manufacturers (inter alia General Electric) have been offering appliances, which combine a PET scanner with a computed tomography scanner (CT) as two “modalities”. Such a combination of PETs with MRI appliances is also planned for the near future.
This raises the question of the spatial arrangement of these two modalities. It is possible to arrange the two gantries in series and move the patient through the two detectors, one after the other. However, such an arrangement allows only time delayed acquisition of those body parts and is thus undesirable. For simultaneous operation of both modalities, closer spatial coupling of both modalities is required. One possible system component arrangement is to fit the PET detectors effectively within the other appliance, that is to say within the MRI for example, for instance between the GC and BC. However, such installation is complicated. A separate PET tube or PET ring offers great advantages with respect to maintainability and production. However, the main difficulties with such an approach are:                Only very limited space is available for attaching the tube, moreover “radial installation space” is very expensive in MRIs.        There is little space for a heat shield within the PET component; however, said heat shield is required due to the adjacently arranged GC, whose surface temperature can reach up to 80° C.        The proximity of the PET component to the oscillating GC leads to vibrational coupling between the two via airborne sound and/or structure-borne sound; this not only causes a noise problem, but can also lead to a reduced service life of the PET component and impairment of its operation.        There is thermal coupling to the GC, which can moreover be subject to surface temperature fluctuations. The PET electronics react sensitively to both temperature fluctuations and excessive temperature increases. Temperature fluctuations result in the deterioration of the signal and in noise.        